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    Oil consumption /Engine rebuild woes

    Hi guys….. looking for some opinions and advice on the below issue I’m experiencing with my M20.

    Engine started to blow blue smoke during acceleration and start up in the morning so I decided to take her out and have the head rebuilt and the rings changed.

    During the build process I sent the head off to a reputable company to have it completely reworked; Pressure testing, cleaned, new guides, new stem seals, lap vales and a minimum skim. Was told that the original stem seals were in a bad way.

    As per the block I had the crank re-grinded/polished, block honed, new big end/main bearings and new piston rings.

    I rebuilt the block myself ensuring the pistons were the correct way up and spaced at 120 degrees…. Etc

    I had the engine back in the car last year and covered around 4k miles but I was still burning oil around 1qrt for 600miles - things started to get bad as the spark plugs fouling, back fire during start up etc.

    A couple of weeks back I carried out a compression test which resulted to Cylinder 3 and 5 having compression low as 135psi and the rest at over 200psi. Spark plug on cylinder 3 was really fouled with oil similar to spark plug 5.

    I also carried out a cylinder leak down test which did not prove anything as for all cylinders the leakage was around 10% max.

    So this weekend end gone I ripped the head off to inspect what could be causing this and here are my findings:
    1. 1. Inspected the cylinder head for any damage/cracks etc and all seems fine.
    2. 2. Nice seal around each cylinder chambers on the head as the head gasket had sealed nicely.
    3. 3. Nice carbon build up on all valves and pistons apart from cylinder 3 and 5 – carbon was wet (oily).
    4. 4. Stripped head and checked play on inlet/exhaust vales on cylinder 3 and 5 which was minimal comparing it to cylinder 1 (good cylinder).
    5. 5. Checked whether the valves were lapped correctly by putting the head upside down and having all valves closed and pouring water to see any leakage – this was all fine, no water leaked through proving the valves were lapped correctly.
    6. 6. Next I slowly took out piston 3, 5 and 1(good Piston) ensuring that there was minimal movement on the rings. All rings were intact and identical to piston 1 which is the good piston.
    7. 7. On cylinder 3 the spacing of the rings were quite close approx. 20degrees – I'm assuming that the rings spin during combustion.


    With all the above checked I am a little stumped of what could be causing the oil consumption/ spark plugs fouling on 3 and 5?

    As I have spent a lot of time, effort and money on this engine so fat rim not looking to replace it as I would like to resolve the issue.

    Any feedback would be appreciated!

    #2
    did you check the bores for wear? stem seals good? any excess carbon on top of valves cyl 3 or 5
    89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

    new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

    Comment


      #3
      Are your injectors in good condition? They could be washing your cylinders a bit if they aren't atomizing well. If your spark plug wires are on the way out, you might be fouling due to weak spark. What oil are you using? Did you check the cylinder bore diameters at the top, middle and bottom? What plugs are you using? Got any oil leaks? Maybe you have several smaller unrelated issues going on and you just need a bit more break in. I would suspect that the compression test process is where you have some of the low numbers coming from. The tester may not have been installed the same on 3 and 5. Any helicoils in spark plug holes? I'd suggest using Mobil1 15W50 and put the whole thing back together and use some copper permatex head gasket sealer and enjoy the car and do a compression test again in 1000 miles.

      Comment


        #4
        Thanks guys for the feedback, please see my response below
        1. As per the bores there are no visible lips, scoring however I am planning to check the tolerances this weekend using a bore gauge on the effected bores and using cylinder one for comparison.
        2. Stem seals were replaced 4k miles ago by the workshop and are in good order.
        3. The carbon build up on top of valves 3 and 5 is no more than the ones on cylinder 1.
        4. I had all 6 injectors rebuilt during the build, I don’t have the results details to hand but there were all in excellent working order.
        5. I used brand new NGK BPR6ES spark plugs when I put the engine back together.
        6. I used 15/50 mineral oil during the break in period (approx. 500miles) then replaced the filter and oil to 15/40 semi synthetic.
        7. No helicoils used on the spark plugs nor are there any oil leaks.


        Really disappointed as I have had to rip everything out again to look for this god forsaken oil burning issue and would like to have it completely resolved before putting it back together again.

        Comment


          #5
          The specs for cylinder wear are in the Bentley manual. The rings should have installed with gaps 120 deg apart. The should not rotate once the piston is installed.

          NGK BPR6ES are not a good choice for this engine. A much better plug is the NKG ZGR5A. Unless it has been replaced within the last 10 years, the ignition system could be a player in this. Use OE or OEM distributor cap, rotor and wires.
          The car makes it possible, but the driver makes it happen.
          Jim Levie, Huntsville, AL

          Comment


            #6
            the rings do rotate and oscilate when the engine is running and at different rates, this is actual normal and neccesary
            89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

            new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

            Comment


              #7
              Originally posted by digger View Post
              the rings do rotate and oscilate when the engine is running and at different rates, this is actual normal and neccesary

              This is what impression I had of the rings rotating when the engine is running. As i found it suspicious the ring gaps quite close when i removed the pistons. I am 110% that i set them at 120 degrees.

              All my ignition setup including leads, dizzy and rotor is oem. Dizzy and rotor was changed couple years back and during the build i had lightly rubbed down the points.

              If there was a flaw in the leads for cylinder 3 and 5 and oil was coming through to the combustion chamber, with working leads the oil will still enter the combustion chamber and still burn the oil thus still giving me oil combustion??

              Comment


                #8
                there are lots of SAE papers proving it happens and looking at the effects of bore distortion etc on ring rotation, the speeds can get upto 10rpm apparently. most commonly measurements show its its slower than this. this is one reason why there are recommended cross hatch patterns as this seems to be one driver for the rotation. so too shallow of an angle and the rings dont rotate enough.

                the plug could be fouled with a faulty ignition system but not by oil. it would appear slightly diffferent

                do you still have the valve cover breather going to intake or is it vented to atmosphere?

                would have been good if you did a wet compression test before pulling it apart
                89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

                Comment


                  #9
                  Hi Digger,
                  1. Yes still have the valve cover breather to the inlet...
                  2. I did also carry out wet compression test i will post up the results this weekend (as they are on a piece of paper in the car).


                  Do you have the bore size tolerances to hand? Piston size is 84mm.

                  The plan for this weekend is to check/measure the bore size and see if they are in tolerance.

                  Comment

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